1. Field of the Invention
The present invention relates to the charging of coke ovens with coal.
More particularly, the invention relates to the charging of preheated coal into coke ovens.
Still more specifically, the present invention relates to a method of charging coke ovens with preheated coal, and to an apparatus for carrying out the method.
2. The Prior Art
Coke is made by charging particulate coal, usually a mixture of high-volatile and low-volatile coals, into coking ovens wherein the coal is then converted into coke by destructive distillation. The coal charge is admitted through charging holes in the ceiling of the coke ovens by means of suitable devices.
The number of charging holes and the physical characteristics of the coal have a definite bearing on the time required for charging the oven with the coal. A minimum charging time is particularly desired for many reasons ("The Making, Shaping and Treating of Steel," United States Steel Corporation, 8th Ed., p. 107).
Conventionally the coal is charged into coke ovens as wet coal. This is charged into the oven at the conventionally accepted rate of about 4-6 t/min and forms hills and valleys in the oven chambers; the charge must therefore, on completion of its admission, be leveled. Depending upon the characteristics of the coal and/or its moisture content, a substantial amount of such leveling may be required. This is time-consuming. Furthermore, excessive leveling tends to pack the coal along the top of the coal charge, particularly under the charging holes, thus increasing the bulk density and heat requirements in this area. Excessive leveling may also cause local erosion of the oven wall (ibid).
During the past decade it has been proposed to preheat the particulate coal before charging it into the coke oven. This proposal achieves a remarkable improvement in the coke oven efficiency and the quality of coke produced, even when lower-quality coking coal is utilized for the charge in view of the continuously decreasing world-wide availability of high-quality coal.
From the oven-charging viewpoint, the use of preheated coking coal provides still another advantage. The flow properties of preheated particulate coal differ substantially from those of wet coal, since the adhesion forces between the individual coal particles are much lower than is the case with wet coal. This has made it possible to fill coke oven chambers via only two filling holes at the conventional 4-6 t/min charging rate and yet to achieve a relatively uniform charging of the chamber to a high level without requiring subsequent leveling of the charge, since due to its good flow properties the preheated coal charge tends to level itself.
However, as already indicated, a minimum charging time is one of the very important aspects of coke oven operation, not only in terms of operating economy but also in view of the reduction in environmental pollution attendant upon every charge-time reduction. Further reductions in the required charging time, and improvements in the uniformity of charging and in the utilization of the chamber volume, are therefore desirable.